Unicode input outwith BMP not working in samterm

[nelk114]

Inputting characters outwith the Basic Multilingual Plane is broken, at least on X11. Both using Compose‐key sequences and changing my keyboard layout (using xkbcomp) to enter high characters projects the character onto the BMP (e.g. typing U+1D15F ⟨𝅘𝅥⟩ gives U+D15F ⟨텟⟩).

sam -d in a unicode‐capable terminal emulator (in my case st) handles it fine so sam itself isn't the issue. I'd hazard a guess that it's a bug in libXg?